Supersonic Cooling Nozzle with Airfoils

ABSTRACT

A supersonic cooling system, as disclosed herein, operates by pumping liquid. Because the supersonic cooling system pumps liquid, the cooling system does not require the use of a condenser. The cooling system utilizes a compression wave to facilitate a phase change utilized in the cooling effect generated by the system. An evaporator operates in the critical flow regime in which the pressure in one or more evaporator nozzles will remain almost constant and then ‘shock up’ to the ambient pressure. The evaporator may be provided with airfoils to improve characteristics of the fluid flow, thereby increasing efficiency of the system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to cooling systems. The invention relates more particularly to supersonic cooling cycles utilizing nozzles with airfoils.

2. Description of the Related Art

Vapor compression systems are used in many cooling applications such as air conditioning and industrial refrigeration. A vapor compression system generally includes a compressor, a condenser, an expansion device, and an evaporator. In a prior art vapor compression system, a gas in a saturated vapor state is compressed to raise the temperature of that gas, the gas then being in a superheated vapor state. The compressed gas is then run through a condenser and turned into a liquid, and heat is rejected from the system. The condensed and liquefied gas is then taken through an expansion device, which drops the pressure and the corresponding temperature. The resulting refrigerant is then boiled in an evaporator, with the refrigerant absorbing heat. The saturated vapor is then returned to the compressor.

FIG. 1 illustrates a vapor compression system 100 as might be found in the prior art. In the prior art vapor compression system 100 of FIG. 1, compressor 110 compresses the gas to (approximately) 238 pounds per square inch (PSI) and a temperature of 190° F. Condenser 120 then liquefies the heated and compressed gas to (approximately) 220 PSI and 117° F. The gas that was liquefied by the condenser 120 is then passed through the expansion valve 130 of FIG. 1. By passing the liquefied gas through expansion value 130, the pressure is dropped to (approximately) 20 PSI.

A corresponding drop in temperature accompanies the drop in pressure, which is reflected as a temperature drop to (approximately) 34° F. in FIG. 1. The refrigerant that results from dropping the pressure and temperature at the expansion value 130 is boiled at evaporator 140. Through boiling of the refrigerant by evaporator 140, a low temperature vapor results. The vapor is illustrated in FIG. 1 as having a temperature of (approximately) 39° F. and a corresponding pressure of 20 PSI.

The cycle carried out by the system 100 of FIG. 1 is an example of a vapor compression cycle. Such a cycle generally results in a coefficient of performance (COP) between 2.4 and 3.5. The COP, as illustrated in FIG. 1, is the evaporator cooling power or capacity divided by compressor power. It should be noted that the temperature and PSI references that are shown in FIG. 1 are exemplary and are for the purpose of illustration only.

FIG. 2 illustrates the performance that might be expected of a vapor compression system similar to that illustrated in FIG. 1. The COP illustrated in FIG. 2 corresponds to a typical home or automotive vapor compression system operating at an ambient temperature of (approximately) 90° F. The COP shown in FIG. 2 corresponds to a vapor compression system utilizing a fixed orifice tube system.

A system like that illustrated in FIG. 1 typically operates at an efficiency rate or COP that is far below that of system potential. To compress gas in a conventional vapor compression system like that illustrated in FIG. 1 (system 100) typically takes 1.75-2.50 kilowatts for every 5 kilowatts of cooling power. This exchange rate is less than optimal and directly correlates to the rise in pressure times the volumetric flow rate. Degraded performance is similarly and ultimately related to performance (or lack thereof) by the compressor 110.

Haloalkane refrigerants such as tetrafluoroethane (CH₂FCF₃) are inert gases that are commonly used as refrigerants in refrigerators and automobile air conditioners. Tetrafluoroethane has also been used to cool over-clocked computers. These gases are referred to as R-134 gases. The volume of an R-134 gas can be 600-1000 times greater than its corresponding liquid form. This multiplier shows that the theoretical efficiency of a system utilizing an R-134 gas is much higher than is currently being realized, and evidences the need for an improved cooling system that more fully recognizes system potential and overcomes technical barriers related to compressor performance.

SUMMARY OF THE CLAIMED INVENTION

A first claimed embodiment of the present invention is for a supersonic cooling system utilizing a pump to assist fluid flow in a fluid flow path. The fluid flow path has both a high pressure region and a low pressure region. The system further includes an evaporator in the fluid flow path. The fluid travels at a velocity that is equal to or greater than the speed of sound in at least a portion of the evaporator. At least one airfoil is positioned in the evaporator to modify the flow of fluid within the evaporator.

A second claimed embodiment of the present invention is for a method that includes pumping a fluid through a fluid flow path. The fluid flow path includes an evaporator in which the fluid flows at a critical flow rate. The method further includes modifying a flow of the fluid with at least one airfoil positioned in the fluid flow path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vapor compression cooling system as may be found in the prior art.

FIG. 2 is a pressure—enthalpy graph for a vapor compression cooling system like that illustrated in FIG. 1.

FIG. 3 is a schematic diagram of a supersonic cooling system.

FIG. 4 is a sectional view of an evaporator tube/nozzle as may be utilized in the supersonic cooling system of FIG. 3.

FIG. 5 is a front view of an evaporator equipped with an airfoil assembly.

FIG. 6 is a partially broken view of the evaporator tube/nozzle with an airfoil assembly.

FIG. 7 is a top plan view of an airfoil.

FIG. 8 illustrates a method utilized in the supersonic cooling system.

DETAILED DESCRIPTION

FIG. 3 illustrates an exemplary supersonic cooling system 300 in accordance with an embodiment of the present invention. The supersonic cooling system 300 of FIG. 3 operates by pumping liquid. Because the supersonic cooling system 300 pumps liquid, the system 300 does not require the use of a condenser 120 as does the prior art vapor compression system 100 of FIG. 1. Supersonic cooling system 300, instead, utilizes a compression wave. The evaporator of supersonic cooling system 300 operates in the critical flow regime where the pressure in an evaporator nozzle will remain almost constant and then ‘shock up’ to the ambient pressure.

The supersonic cooling system 300 of FIG. 3 recognizes improved efficiencies over prior art cooling systems (e.g. FIG. 1) in that the pump 310 of the system 300 does not, nor does it need to, draw as much power as the compressor 110 in the prior art compression system 100 of FIG. 1. A supersonic cooling system designed according to an embodiment of the presently disclosed invention may recognize exponentially improved pumping efficiencies even though the supersonic cooling system also utilizes a vapor compression cycle. For example, where a prior art compression system 100 may require 1.75-2.5 kilowatts for every 5 kilowatts of cooling power, a supersonic cooling system 300 like that illustrated in FIG. 3 may pump liquid from 14.7 to 120 PSI with a pump 310 drawing power at approximately 500 W.

The cooling cycle of the cooling system 300 may begin with the pump 310 raising the pressure of the working fluid being used by system 300 from, for example, 20 PSI to 100 PSI or more, to establish a high pressure region of the system 300. In some embodiments of the system 300 the temperature of the working fluid may, at this inlet section of the system 300, be approximately 95° F.

In cooling systems utilizing more than one evaporator tube or nozzle, the pump 310 may direct fluid into a manifold 320 that feeds the evaporator 330. The manifold 320 may supply a plurality of evaporator tubes or nozzles 400 (see FIG. 4) in the evaporator 330.

As the working fluid is introduced to the evaporator 330, the evaporator 330 induces a pressure drop e.g., to approximately 5.5 PSI, to establish a low pressure region. A concurrent phase change results in a lowered temperature in the working fluid, creating the cooling effect. The evaporator 330 of system 300 operates in the critical flow regime of the working fluid in which the fluid is accelerated to a velocity equal to or greater than the speed of sound in the fluid. The pressure drop establishes a compression wave that assists in the acceleration of the working fluid.

The evaporator 330 may also induce cavitation in the working fluid to assist in the invocation of the phase change. The cavitation also serves to reduce the speed of sound in the working fluid. Further explanation of the cavitation effect is provided below in the description of the evaporator nozzle 400.

As the working fluid is accelerated and undergoes a pressure drop and phase change, the working fluid further ‘boils off’ in evaporator 330, providing a cooling effect. In embodiments in which the working fluid is water, the water may be cooled to 35-45° F., or approximately 37° F. At or near the exit of the evaporator 330, the fluid may ‘shock up’ to approximately 20 PSI.

To facilitate the dissipation of heat in the system 300, the evaporator 330 may be thermally coupled with a heat exchanger 340. The heat exchanger 340 may operate with a coolant fluid, the coolant fluid being circulated around or through an area or an object to be cooled. The heat exchanger 340 then brings the warmed coolant fluid into thermal communication with the working fluid cooled in the evaporator 330. The working fluid of the system 300 may be at a temperature of approximately 90-100° F. after the working fluid exits evaporator 360, receives heat from the area or object to be cooled, and returns to the inlet of pump 310.

FIG. 4 is a cross sectional view of an exemplary evaporator nozzle 400 as may be utilized in the evaporator 330. The nozzle 400 may be an annular flow converging—diverging nozzle, as illustrated in FIG. 4. The nozzle 400 includes an inlet 420 and a diverging portion 440 formed inside the nozzle body 410. A throat section 430 causes the working fluid to accelerate to a speed equal to or greater than the speed of sound in the working fluid after the working fluid enters the nozzle 400. The acceleration of the working fluid through the throat section 430 causes a sudden drop in pressure, which may result in cavitation. These factors may assist in the formation of the compression wave in the evaporator nozzle 400. The fluid is accelerated further, to supersonic speeds, as the fluid passes through the diverging portion of the nozzle 400.

The supersonic flow of the working fluid through the evaporator nozzle 400 induces a pressure drop and phase change in the working fluid that results in a lowered temperature, providing the cooling effect of the cooling system 300. The pressure change may span a range of approximately 20 PSI to 100 PSI. In some instances, the pressure may be increased to more than 100 PSI, and in some instances, the pressure may be decreased to less than 20 PSI. The pressure change of all the cooling systems described herein may be in this range of change, or may exceed the range described immediately above.

The choking effect of the nozzle throat section 430 on the fluid flow may be amplified by installing an assembly including a conical central body 450. The central conical body 450 supports one or more airfoils 460. In addition to the sectional view illustrated in FIG. 4, additional perspective views of the airfoil assembly may be seen in FIGS. 5 and 6. Various implementations of the assembly may utilize a plurality of airfoils 460 mounted on the central body 450. For example, in the embodiment described in the context of FIGS. 5 and 6, sixteen airfoils 460 are mounted on the surface of the central body 450. The airfoils may be positioned so that a distance between the airfoil 460 and a wall of the nozzle 400 is uniform for each airfoil 460, i.e., a centerline of the central body 450 is colinear with a centerline of the evaporator. This positioning provides a balanced fluid flow path through the airfoils 460.

As illustrated in FIG. 7, a central body 710 of each of the airfoils 460 includes a rounded leading edge 720. The broadest portion of each airfoil 460 is near the leading edge 720. Viewed from above as in FIG. 7, the airfoils 460 taper downward from the broadest width near the leading edge 720 to a narrow trailing edge 730. The volume that the fluid encounters as it flows along the tapered airfoils 460 therefore expands from the maximum airfoil thickness near the leading edge 720 to the trailing edge 730 of the airfoils 460.

The airfoils 460 may be positioned so that the locations of maximum airfoil thickness near the leading edges 720 are aligned with a throat of the nozzle 400. The areas of maximum airfoil thickness near the leading edges 720 choke the fluid flow as the working fluid flows through the airfoil assembly. As the fluid flows along the tapered central body 710 of each airfoil 460, the expanding available volume assists the expansion of the working fluid as it flows at supersonic speed.

In operation, when the working fluid enters the throat portion 430 of the evaporator nozzle 400, the working fluid is first choked as it flows into the airfoil assembly and around the areas of maximum airfoil thickness near the leading edges 720 of the airfoils 460. The working fluid is then accelerated to high (sonic or supersonic) speed as it flows along the main bodies 710 of the airfoils 460. The inlet pressure, the diameter of the throat orifice, and the configuration of the airfoil assembly may be selected so that the speed of the working fluid at the entry of the throat portion 430 is approximately the speed of sound (Mach 1).

As the working fluid is accelerated by the airfoils 460 situated in the nozzle 400, the fluid undergoes a sudden drop in pressure. The pressure differential generates cavitation that commences at the boundary between the exit of the inlet portion 420 and the entry to the throat portion 430. Cavitation is also triggered along the wall of the throat portion 430. Cavitation results in bubbles of the working fluid in the vapor phase being present within the fluid in the liquid phase, thereby providing a multi-phase working fluid. The creation of such vapor bubbles requires the input of energy for the input of latent heat of vaporization and as a result the temperature falls. At the same time, the reduction in pressure together with the working fluid achieving a multi-phase state causes the local speed of sound in the working fluid to be lowered, with the result that the working fluid passes over the airfoils 460 and exits the throat portion 430 at a supersonic speed. The supersonic speed may be, for example, Mach 1.1 or higher. It is noted that the reduction in the localized speed of sound changes the character of the flow from traditional incompressible flow to a regime more in character with high speed nozzle flow.

As the working fluid travels across the airfoils 460 within the expanding interior of the nozzle body 410, the pressure remains at a low level and the fluid expands. As a result of the expansion, the flow accelerates further, reaching a speed on the order of, for example, approximately Mach 3.

As the fluid accelerates and pressure is reduced, the local static pressure drops, so that more vapor is generated from the surrounding liquid working fluid. As the working fluid moves below the saturation line, the cooling effect required for the cooling system is generated and the flow behaves as if it was in an over-expanded jet. Once the working fluid has picked up sufficient heat, and due to frictional losses, the fluid shocks back to a subsonic condition and returns to ambient conditions as it exits the nozzle 400.

The method utilized in the supersonic cooling system 300 is illustrated in FIG. 8. In step 810, the pressure of a liquid, the working fluid, is raised. The pressure may, for example, be raised from 20 PSI to in excess of 100 PSI. The pressure increase may be to 300 PSI or even 500 PSI.

In step 820, fluid flows through the nozzle/evaporator tube(s), directed by the airfoils 460. Flow across the airfoils 460 accelerates the working fluid. A pressure drop and phase change result in a lowered temperature as the working fluid is boiled off in step 830.

Critical flow rate, which is the maximum flow rate that can be attained by a compressible fluid as that fluid passes from a high pressure region to a low pressure region (i.e., the critical flow regime), allows for a compression wave to be established and utilized in the critical flow regime. Critical flow occurs when the velocity of the fluid is greater or equal to the speed of sound in the fluid. In critical flow, the pressure in the channel will not be influenced by the exit pressure and at the channel exit, the fluid will ‘shock up’ to the ambient condition. In critical flow the fluid will also stay at the low pressure and temperature corresponding to the saturation pressures. In step 840, after exiting the evaporator tube, the fluid may “shock” up to approximately 20 PSI or another pressure, depending on the specific application. In a step 850, cooling via heat exchange may be accomplished.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. The descriptions are not intended to limit the scope of the invention to the particular forms set forth herein. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments. It should be understood that the above description is illustrative and not restrictive. To the contrary, the present descriptions are intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and otherwise appreciated by one of ordinary skill in the art. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. 

1. A supersonic cooling system, comprising: a pump to facilitate a flow of a fluid through a fluid flow path having both a high pressure and a low pressure region; an evaporator in the fluid flow path, wherein the fluid accelerates to a velocity that is equal to or greater than the speed of sound; and at least one airfoil positioned in the evaporator to modify the flow of fluid within the evaporator.
 2. The supersonic cooling system of claim 1, wherein a width of the airfoil tapers downward from a thickest portion to a trailing edge so that the airfoil chokes the flow of the fluid at the thickest portion and accelerates the flow along a main body toward the trailing edge.
 3. The supersonic cooling system of claim 1, wherein a central body is positioned in the fluid flow path in the evaporator to support multiple airfoils.
 4. The supersonic cooling system of claim 3, wherein each of the multiple airfoils further comprises a leading edge, the leading edges of the airfoils choking the flow of the fluid.
 5. The supersonic cooling system of claim 4, wherein a width of each airfoil tapers downward from a thickest portion to a trailing edge so that the flow path volume expands from the thickest portions to the trailing edges of the airfoils to accelerate the flow of the fluid.
 6. The supersonic cooling system of claim 3, wherein a centerline of the central body is colinear with a centerline of the evaporator to provide a balanced fluid flow path through the airfoils.
 7. The supersonic cooling system of claim 1, wherein the airfoil is oriented so that a thickest portion of the airfoil is aligned with a throat of an evaporator nozzle of the evaporator to provide a choke point at or near a leading edge of the airfoil.
 8. The supersonic cooling system of claim 1, wherein the evaporator is located in the low pressure region of the fluid flow path, and the evaporator facilitates a phase change of the fluid.
 9. The supersonic cooling system of claim 1, wherein fluid flow in the evaporator is in a critical flow regime of the fluid.
 10. The supersonic cooling system of claim 1, wherein the system maintains a substantially constant pressure in the fluid flow path in the evaporator, the fluid shocking up to an elevated pressure as the fluid exits the evaporator.
 11. The supersonic cooling system of claim 10, wherein the system maintains a substantially constant enthalpy as the fluid shocks up to the elevated pressure.
 12. The supersonic cooling system of claim 1, wherein the system maintains a substantially constant enthalpy as the pressure of the fluid is decreased.
 13. The supersonic cooling system of claim 1, further comprising a heat exchanger in thermal communication with the fluid.
 14. A supersonic cooling method, comprising: pumping a fluid through a fluid flow path, the fluid flow path including an evaporator wherein the fluid flows at a critical flow rate; and modifying a flow of the fluid with at least one airfoil positioned in the fluid flow path to accelerate the flow of the fluid.
 15. The supersonic cooling method of claim 14, wherein the flow of the fluid is modified by multiple airfoils secured to a central body positioned in the fluid flow path in the evaporator.
 16. The supersonic cooling method of claim 14, wherein the flow of the fluid is choked by the airfoil.
 17. The supersonic cooling method of claim 14, wherein the fluid expands as it travels along portions of a main body between the leading edge and a trailing edge of the airfoil.
 18. The supersonic cooling method of claim 14, wherein the evaporator facilitates a phase change of the fluid.
 19. The supersonic cooling method of claim 14, wherein the flow of the fluid in the evaporator is accelerated to a velocity equal to or greater than the speed of sound in the fluid.
 20. The supersonic cooling method of claim 14, further comprising transferring heat to the fluid via a heat exchanger. 